Download Lecture Two: Systema Naturae "Did King Philip come over from

Lecture Two: Systema Naturae
Why Classify?
An aid to memory: It's easier to remember the characteristics of an entire group of rganisms
than to recall the characters of individual organisms over and over!
An aid to prediction: If one knows that all members of a particular taxon have aparticular
set of characteristics, then there's a good bet that a *new* member of thattaxon may have
some of those (useful?) characteristics, too. (such as antibiotic production, edibility, etc.)
An aid to explaining evolutionary relationships
Provides a relatively stable system of Internationally recognizable names. (A group of
organisms classified together at any level is called a taxon.)
A character is some physical aspect of a taxon that gives clues about its evolution:
morphological (fur color, scale shape, number of toes, etc.)
molecular (DNA sequence, RNA sequence, amino acid sequence of proteins)
Taxonomy -done by taxonomists, is the science of naming and classifying organisms
Systematics -done by biosystematists, is the science of determining evolutionary
relationships among organisms. (Most biosystematists are also taxonomists.)
A taxon’s evolutionary history is its phylogeny, and it can be represented as a branching
diagram called a phylogenetic tree.
Earliest studies of biodiversity had nothing to do with evolution:
• classifications were based on subjective logic
• system of ordering "like" organisms which reflected a "natural order" (kosmos)
• scientific names were long, cumbersome sentences that described the organism.
1758 -Carl Linne (Swedish botanist) published Systema naturae, outlining the system of
binomial nomenclature we still use today. (He even renamed himself, in the Latinized
fashion required of his system, Carolus Linnaeus. Today, we fondly remember him and
refer to him as the great Linnaeus.)
A scientific name in Systema naturae consists of Genus and species:
Oryctolagus cuniculus (domestic rabbit), Homo sapiens (human), Canis familiaris, (dog).
Every species has its own, unique scientific name.
WHAT IS A SPECIES? There are many definitions, but the biological definition is:
"A group of similar organisms able to interbreed in nature to produce fertile, viable offspring."
(This means that they are REPRODUCTIVELY ISOLATED from other species: they
cannot produce fertile, viable hybrids with other species.)
Remember the old mnemonic device:
"Did King Philip come over from Germany soaked?"
Domain  Kingdom  Phylum  Class  Order  Family  Genus  species
EACH SPECIES IS NESTED IN AN ENTIRE HIERARCHY, FROM DOMAIN (largest, most
inclusive taxon+) DOWN THROUGH SPECIES (smallest, least inclusive taxon).
There are THREE DOMAINS of living things:
Bacteria – unicellular prokaryotic organisms (“true” bacteria)
Archaea – unicellular prokaryotes more closely related to us than bacteria are
Eukarya – unicellular and multicellular organisms made of eukaryotic cells (protists,
fungi, plants, and animals)
PROKARYOTIC CELL lacks a membrane-bounded nucleus or membrane-bounded
organelles. (Bacteria and Archaea)
EUKARYOTIC CELL has a membrane-bounded nucleus and membrane-bounded
organelles. (Eukarya: Animalia, Fungi, Plantae and many kingdoms of protists)
Related species are placed in the same GENUS. Related Genera (plural of genus) are
grouped in the same FAMILY. Related Families are all placed in the same ORDER. Related
Orders are all grouped in the same CLASS. Related Classes are placed in the same
PHYLUM. Related Phyla are classified in the same KINGDOM. Related Kingdoms are
placed in the same DOMAIN.
And those long, complicated species names actually *mean* something!
Eleutherodactylus planirostris (Greenhouse Frog)
eleutheros = "free" plani = "flat" dactyl -"digit" rostris -"nose" …this is a little frog with
unwebbed toes ("free toes"), and he has a flat nose!
Proper names are okay to use, but they, too, must be Latinized:Chilomeniscus savagei :
chilo = "lip" meniscus -"crescent"
This is a little snake with a snub-nosed, crescent shaped lip that reminded the person who
described this snake of his mentor, Professor Jay Savage. So he named the snake after Dr.
Savage by Latinizing Dr. Savage's name, and making it into the snake's specific epithet
(that's the species part of the scientific name).
What do scientists use to classify organisms?
Fossil record? -Surprisingly NO. The fossil record is not a good tool for this.
Comparative anatomy (morphology)
Comparison of proteins
Comparison of embryonic development
Comparison of genetic material (chromosomes, DNA and RNA)
Primitive versus Derived characters
A primitive character is one that is relatively unchanged from that same character in an
ancestral species. A derived character is one that is rather different and changed from that
same structure in an ancestral species.
NOTE THAT THESE ARE COMPARATIVE TERMS. A structure or character can be
considered "primitive" or "derived" only if you're comparing it to something else.
Example: In comparison to the non-fully opposable thumbs of other primates, the fully
opposable thumb of a human is derived. (That is, it's changed from the primitive, ancestral
form of the thumb, which was not opposable at all!)
Another example: The vertebral column and bony cranium (skull) of a human are both
primitive characters that a human shares with all other vertebrates. (That is, the presence of
a spinal column and bony cranium is primitive to all vertebrates: like the ancestral
vertebrate, all vertebrates have them!)
Homologous versus Analogous characters
AGAIN, THESE ARE COMPARATIVE TERMS. You compare at least two characters (in
two species) to say whether they are homologous or analogous to each other.
A homologous character is one that is found in two different species, and has been
derived from the same ancestral source (which you can tell by following the embryonic
development.
Example: The middle fingernail on your hand is HOMOLOGOUS to the hoof on the front leg
of a horse! If you follow the embryonic development of a human and a horse you will see
that the same cells/tissues that give rise to the fingernail in a human give rise to the hoof in
the horse! This means that the most recent common ancestor of the human and the horse
(which was a vertebrate, and a mammal) had this original structure, though it has evolved
into different things in its human and horse descendants of that common ancestor. An
analogous character is one which is found in two different species, serves a similar
function in both species, but IS NOT derived from the same ancestral source (which you
can again tell by following the embryonic development).
Example: The wing of a bird and the wing of a butterfly both allow the animal to fly.
However, the most recent common ancestor of the bird and the butterfly (which was neither
a bird nor a butterfly, but something that was little more than a blob of cells with a mouth)
did not have wings! This means that the bird wing and the butterfly wing evolved
independently, from different embryonic sources, even though they serve the same
function.
When two characteristics evolve superficial similarity due to similar environmental
pressures, CONVERGENT EVOLUTION is said to have taken place. (Another example:
Both the shark and the dolphin have a torpedo shape because this allowed their ancestors
to survive well and reproduce in an aquatic environment. However, the most recent
common ancestor of shark and dolphin (a fishlike animal) gave rise to sharks on one branch
of its family tree, and to terrestrial, four-legged animals on another branch. Dolphins evolved
from those four-legged descendants of the fish ancestor and SECONDARILY evolved the
torpedo shape, whereas the shark never lost its torpedo shape. Hence, the similar shape of
dolphin and shark arose in different ways, and from different ancestors, and is said to be
due to CONVERGENCE.)
Once a biosystematist has enough information about a species, s/he can construct a
PHYLOGENETIC TREE, which is a diagram of ancestral species giving rise to new
species, and which shows the evolutionary relationships of related species.
Example: A phylogenetic tree of the vertebrate groups
…which can be considered a working hypothesis, and can change as new information
becomes available.
A PHYLOGENETIC TREE shows of hypothetical EVOLUTIONARY RELATIONSHIPS.
A TAXONOMIC KEY is a tool used by a scientist to IDENTIFY SPECIMENS. It may or may
not reflect evolutionary relationships. We'll learn about those next, in today's activity,
"Identifying the Wild Pasta Species of the United States."